1. Field of the Invention
This invention relates to a diaphragm-operated pressure control valve assembly and, more particularly, to improvements in a pressure control valve assembly of the type used in conjunction with a negative pressure source as well as fluid pressure source and including at least one diaphragm, on one surface of which fluid medium pressure is applied and on the other surface of which negative pressure is applied. The valve assembly of the present invention is, moreover, especially designed for use in systems wherein the fluid medium such as gas contains some ingredients such as condensed water.
2. Description of the Prior Art
A diaphragm-operated valve assembly within which variable control pressure is admitted to effect the valve operation has been conventionally proposed. When the gas containing various ingredients is utilized as the variable control pressure applied onto the rubber diaphragm, any objectionable materials contained in the gas should not gather on the diaphragm in order to prevent the possible oxidation or corrosion thereof due to such materials or ingredients.
One system employing such diaphragm-operated valve assembly is, typically, an exhaust gas recirculation system for the internal combustion engines of automotive vehicles. Exhaust gas recirculation is, as is well known, one of the effective means for reducing the emission of oxides of nitrogen (commonly represented as NOx) by the exhaust systems of internal combustion engines. The exhaust gas is, in the exhaust gas recirculation system, employed as fluid medium for actuating the diaphragm of the valve assembly. However, the conventional diaphragm-operated valve assembly leaves much to be desired because the gas ingredients, such as condensed water, are likely to gather within the valve assembly, particularly on the diaphragm; with the results that the diaphragm is subjected to corrosion or oxidation. U.S. Pat. No. 3,802,402 granted on Apr. 9, 1974 to Mr. Peter Phillimore Swatman or U.S. Pat. No. 3,834,366 granted on Sept. 10, 1974 to General Motors Corporation, for instance, disclose the diaphragm-operated valve assembly, but are silent as to the problems caused by the gas ingredients as mentioned above.